When a human-infecting virus or bacterium is treated, the World Health Organization (WHO) guidelines for laboratory biosafety are a basis for stipulating that the treatment be done in a contained environment classified and defined according to danger as biosafety (BS) level 1, BS level 2, BS level 3, or BS level 4. Furthermore, cases in which BS level 2 involves an aerosol or cases of BS level 3 or BS level 4 must be handled in a biosafety cabinet (also referred to as a “BSC” below) suitable for the level.
For cases dealing with genetically modified organisms, it is also stipulated that the organisms be treated in a BSC for containment, as the Cartagena Protocol on Biosafety (an agreement on biological diversity) has come into effect.
Furthermore, a BSC requires periodic maintenance in order to continually use the BSC safely. Before maintenance is performed, the interior of the BSC must be decontaminated for the purpose of preventing worker infection and preventing exposure to harmful microorganisms.
In addition to the above, JIS K 3800:2009 stipulates that a BSC interior be decontaminated in the following cases.
a) Before a periodic inspection or safety check
b) Before a HEPA filter replacement
c) Before the cabinet is moved
d) When the interior has been heavily contaminated
e) When the intended purpose has changed
f) In other necessary cases
The range of BSC decontamination includes the inside of a work area, a circulated air HEPA filter, an exhaust HEPA filter, and the inside of a duct leading to these HEPA filters (also referred to as “the interior of the BSC” below).
For many years since 1939 when BSCs came into use, formalin fumigation has been used to decontaminate the interiors of BSCs (Non-Patent Document 1).
Formalin fumigation is performed by a procedure of heating and fuming a small amount of paraformaldehyde and water in the condition of rigorous curing. A BSC fan is sometimes operated to fill the BSC interior with formalin. After leaving the BSC for approximately one day in this state, neutralization and exhausting are performed.
Furthermore, when paraformaldehyde crystals thereafter adhere to surfaces inside the BSC as white powder, the surfaces must be repeatedly wiped with water many times because the crystals are toxic and corrosive. This decontamination work requires approximately two days.
Formalin fumigation of BSC interiors has been used for at least 70 years up to the present day. However, in formalin fumigation, vapor containing formaldehyde is created, and this vapor is harmful to the human body and is designated as a deleterious substance not for medicinal use under the Poisonous and Deleterious Substances Control Law of Japan. Formaldehyde is also specified as a specific class I designated chemical substance (a carcinogen) under the 2012 Chemical Substances Management Act of Japan. In recent years, this substance has been specified by the World Health Organization as a substance that causes leukemia and lymphoma. Verifications that this substance is harmful to humans have been made internationally, stipulations in multiple countries have increased, and there is demand for a decontamination method to replace formalin fumigation.
A method of using chlorine dioxide gas and hydrogen peroxide vapor has been developed as an alternative decontamination method.
However, chlorine dioxide gas is highly toxic with a control standard value of 0.1 ppm, a more severe value than a control standard value of formalin, 0.75 ppm. Similar to formalin, chlorine dioxide gas requires rigorous curing and must be neutralized by sodium thiosulfate and exhausted. The device is also expensive at typically 500,000 to 10,000,000 yen.
With a method using hydrogen peroxide vapor, an approximately 35% hydrogen peroxide solution is boiled to create vapor. Hydrogen peroxide vapor, which is highly toxic, requires rigorous curing and has a control standard value of 1.0 ppm. Hydrogen peroxide, said to not be carcinogenic to humans, is not listed in the carcinogens of the IARC, the NTP, or the OSHA, but is classified as A3 (no cases of causing cancer in humans have been confirmed, but carcinogenic effects in lab animals have been established) in the categories of the ACGIH (Non-Patent Document 2). The device is also expensive at typically 4,000,000 to 10,000,000 yen.
Thus, the alternative method of formalin fumigation has many problems in terms of safety and cost, and formalin fumigation remains mainstream.